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Spinal fusions are performed to treat degenerative diseases, deformities, and trauma. These problems generally cause or allow displacement or rotation of a vertebra relative to the adjacent vertebra. The objective of spinal implants is to facilitate realignment and/or fixation of spinal elements for fusion. It has been demonstrated in clinical studies, that surgeries using spinal implants are more effective at providing structure and rigidity to the spine than surgeries in which implants are not used.
The majority of existing spinal implants use metal rods or plates to restrict the relative motion of the adjacent vertebra while fusing. Once the two vertebrae are fused there is no longer a need for the rods or plates, which may later cause complications. Certain implants are absorbed leaving no foreign material. Implant placement and success can be improved by use of distracting or spreading to stretch the attaching ligaments. This stretching of the ligaments is called ligamentotaxis. Ligamentotaxis is used by surgeons to restore the anatomic alignment of the spine, help to maintain the spinal implant in the proper position, and encourage graft incorporation by loading the graft host interface. This patent provides for an improved method and device for the purpose of spreading spinal elements such as vertebrae to accept spinal implants.
A bone fusion, using a threaded cylindrical dowel bone implant, may be performed between two adjacent vertebrae to restore the space originally occupied by a disc. To increase the surface area of contact between the flat vertebral end plates and the cylindrical dowel or the absorbable fixation screw surface, it is necessary to prepare the flat vertebral end plates to a partial cylindrical concave surface.
U.S. Pat. No. 6,080,155 to Michelson is an example of a hollow tube 64 with two protruding tangs 60, shown in FIG. 12, are used for distraction. These tangs are referred to in the literature as extended outer sleeves 64. These tangs are hammered into the disc space to force distraction. Since the tangs are tapered 61, any movement of the tube causes a component of the holding force to tend to dislodge the sleeve. Because of the misalignment angle 63, the tangs do not hold the tube reliably and they allow trapezoidal deformation, especially with the cervical vertebrae, which are smaller than the lumbar vertebrae. U.S. Pat. No. 5,899,908 to Kuslich et al. is an example of cylindrical plug 70 with a bullet nose 71 is used for distraction. The cylindrical distractor is hammered into place by shaft 72. The tangs or cylindrical plugs distract and lift the vertebra by contacting it on the edges at the vertebral protrusions 27. This moves the distractor centerline away from the end plate centerline therefore the end plates are not distracted parallel. The tangs are short compared to the tube length. This results in an unstable tube position during the reaming and tapping procedures.
Another method uses circular tangs 61, which centers on the vertebral end plates as shown in FIG. 13. However to force the dual circular tangs through the intervertebral space requires extreme over distraction as the tang distracts the protrusion 62. This would cause trauma to the vertebrae as well as the tethering ligaments. Once in place the tube is used to guide a sleeve, a reamer, and a thread tap. After the machining is completed the bone dowel can be guided through the tube for implantation.
The purpose of the present invention is to provide a device and a method to distract the flat surfaces on the intervertebral end plates to receive an implant. This device comprises a vertebral cam spreader as shown in various embodiments in the subsequent drawings. The vertebral end plates are spread with the cam spreader appliance in a controlled fashion. The spreader cam is positioned at the center of the vertebral end plates with the spreader in a flat or horizontal position. The cam sections are extended past the vertebral protrusions before beginning to spread the vertebrae. This will provide a controlled uniform spreading, without over spreading, and assure a controlled uniform spacing of the vertebrae. Since the spreader is in the center of the end plates, the centerline of the spreader shaft will coincide with the vertebral end plate centerline. The surgeon can monitor the spreading and can stop and remove the spreader to make adjustments or to change the size of spreader as required at the time of the operation. This cam spreader eliminates the traumatic stress caused by hammering tangs or other distraction devices into place. The disc need not be removed.
The degree of lordosis may be altered by changing the depth of the cam spreader. Various tools can then be attached to or around the cam spread to remove the necessary sections of the disc or vertebrae. For instance, once the vertebrae are spread, a tube with holding tabs is placed over the spreader shaft. The spreader has centering means that will insure that the tube is concentric with the spreader. When the tube is in place, bone screws can be placed through the tabs and into the adjacent vertebra to maintain the vertebral relative position while the tooling and implant are in use. The tube assures that the tools will be centered on and parallel to the vertebral end plates. This in turn can facilitate removing an appropriate amount of material from each adjacent vertebra. After the machining is completed the bone dowel can be guided through the tube and be contained in place with a holding means, preferably a screw thread. These machining and dowel insertion operations are well known to those skilled in the art.
An object of the present invention is to provide a spreader that will distract two vertebrae to place them into preferred positions without over distracting during the process.
Another object of the present invention is to provide an improved method and device for preparing vertebrae for a discectomy, a fusion, and for spinal stabilization.
Another object of the present invention is to provide a method of performing a fusion safer, easier, and in less time than in prior art.
Another object of the present invention is to provide an improved device and a method of performing a spinal fusion and a spinal stabilization using harvested bone, absorbable implants and dowels and metal or nonmetal implants.
Another object of the present invention is to provide devices and methods for cervical, thoracic, and lumbar spinal fusions anteriorly, posteriorly, and/or laterally.
A further object of the present invention is to provide a means for inserting a spinal implant between adjacent vertebrae, while maintaining their optimal spacing, positioning, and alignment.